In the fabrication of semiconductor devices, particularly in the fabrication of sub-micron scale semiconductor devices, profiles obtained in etching process are very important. A careful control of a surface etch process is therefore necessary to ensure directional etching. In conducting an etching process, when an etch rate is considerably higher in one direction than in the other directions, the process is called anisotropic. A reactive ion etching (RIE) process assisted by plasma is frequently used in an anisotropic etching of various material layers on top of semiconductor substrate. In plasma enhanced etching processes, the etch rate of a semiconductor material is frequently larger than the sum of the individual etch rates for ion sputtering and individual etching due to a synergy in which chemical etching is enhanced by ion bombardment.
To avoid subjecting a semiconductor waiver to high-energy ion bombardment, the wafer may also be placed downstream from the plasma and outside the discharge area. Downstream plasma etches more in an isotropic manner since there are no ions to induce directional etching. The downstream reactors are frequently used for removing resist or other layers of material where patterning is not critical. In a downstream reactor, radio frequency may be used to generate long-lived active species for transporting to a wafer surface relocated remote from the plasma. Temperature control problems and radiation damage are therefore significantly reduced in a downstream reactor. Furthermore, the wafer holder can be heated to a precise temperature to increase the chemical reaction rate, independent of the plasma.
In a downstream reactor, an electrostatic wafer holding device known as an electrostatic chuck is frequently used. The electrostatic chuck attracts and holds a wafer positioned on top electrostatically. The electrostatic chuck method for holding a wafer is highly desirable in the vacuum handling and processing of wafers. An electrostatic chuck device can hold and move wafers with a force equivalent to several tens of Torr pressure, in contrast to a conventional method of holding wafers by a mechanical clamping method.
Referring initially to FIG. 1, wherein a conventional inductively coupled plasma etched chamber 10 is shown. In the etch chamber 10, which typically represents one that is commercially available as a LAM TCP etcher, the plasma source is a transformer-coupled source that generates a high density, low pressure plasma away from a wafer surface. The plasma source allows an independent control of ion flux and ion energy. The plasma can be generated by a flat spiral coil (not shown), i.e. an inductive coil separated from the plasma by a dielectric plate 12 which is normally fabricated of a ceramic material with a gas inlet 14 provided therein. The ceramic plate 12 may be a dielectric window made of a substantially transparent material such as quartz to facilitate visual observation of the middle chamber 20. The middle chamber 20 is further formed by a bottom ceramic plate 16 equipped with an apertured opening 18 for allowing a plasma to pass thereto. The sidewall 22 of the middle chamber 20 is normally formed of a metallic material, such as aluminum, with an anodized aluminum surface. The top ceramic plate 12, the bottom ceramic plate 16 and the metallic sidewall 22 form a self-contained chamber, i.e. the middle chamber 20 which has a first cavity 24 therein.
A wafer 30 is positioned on the electrostatic chuck (or ESC) 26 sufficiently away from the RF coil (not shown) such that it is not affected by the electromagnetic field generated by the RF coil. A typical LAM TCP plasma etcher enables a high density plasma to be produced and a high etch rate to he achieved. In the plasma etcher 10, an inductive supply and a bias supply are further used to generate the necessary plasma field. In a typical inductively coupled RF plasma etcher 10, shown in FIG. 1, a source frequency of 13.5 MHZ and a substrate bias frequency of 13.5 MHZ are utilized such that ion density of about 0.5.about.2.0.times.10.sup.12 cm.sup.3 is obtained at the wafer level, while electron temperature of 3.5.about.6.0 eV and a chamber pressure of 1.about.25 mTorr are achieved.
In the plasma chamber 10, after the wafer 30 is etched in the main chamber 32, the chamber is normally evacuated of the etchant gas from the middle chamber 20 and from the main chamber 32 by a turbo pump 34 controlled by a gate valve 36. The turbo pump is further connected to a dry pump 38 through a control valve 42. When the pressure in the chamber is too high, in order not to damage the turbo pump 34, control valve 42 closes while control valve 44 opens to allow the chamber to be evacuated by the dry pump 38 directly. Simultaneous with the pumping process, an inert purge gas such as nitrogen is flown into the middle chamber 20 and the main chamber 32 through gas inlet 14 to further facilitate the removal of residual etchant gas.
In the conventional plasma chamber 10, a problem caused by the residual etchant gas left in the cavity 24 of the middle chamber 20 frequently occurs. The residual etchant gas cannot be evacuated from cavity 24 due to the small holes in the apertured opening 18 situated in the bottom ceramic plate 16. The small holes do not allow a fast flow rate so that the evacuation of the middle chamber 20 is ineffective. The residual etchant gas left in cavity 24 attacks the metal sidewall 22 and thus causing corrosion in the metal. The corrosion of metal, for instance of an aluminum surface, produces particles which contribute to a severe contamination problem for the main chamber 32 where a wafer is positioned.
It is therefore an object of the present invention to provide a plasma etch chamber that does not have the drawbacks or shortcomings of a conventional plasma etch chamber.
It is another object of the present invention to provide a plasma etch chamber that is equipped with a middle chamber that has significantly reduced particle contamination problem.
It is a further object of the present invention to provide a plasma etch chamber that is equipped with a middle chamber and a main chamber which has significantly reduced contamination problem by evacuating residual etchant gas from the middle chamber.
It is another further object of the present invention to provide a plasma etch chamber that is equipped with a middle chamber for feeding an etchant gas plasma into a main chamber that has significantly reduced particle contamination problem.
It is still another object of the present invention to provide a plasma etch chamber that has a middle chamber and a main chamber equipped with a bypass exhaust conduit connecting the middle chamber to the main chamber.
It is yet another object of the present invention to provide a plasma etch chamber that has a middle chamber and a main chamber in fluid communication through an apertured opening and a bypass exhaust conduit.
It is still another further object of the present invention to provide a method for preventing corrosion in an etch chamber by residual etchant gas wherein the etch chamber is equipped with a middle chamber and a main chamber.
It is yet another further object of the present invention to provide a method for preventing particle contamination in an etch chamber by providing a bypass exhaust conduit connecting between a middle chamber and a main chamber such that residual etchant gas can be evacuated from the middle chamber.